1. Field of the Invention
The present invention relates to a semiconductor epitaxy structure, and particularly, to a GaN-based heterostructure photodiode. By doping borons in the activity layer of the PIN photodiode (PIN PD), the band gap between the P type layer and the N type layer will be modulated so as to promote the light receiving ability.
2. Description of the Prior Art
The GaN-based composition semiconductor is mainly used for making the diode, such as light emitting diode (LED), laser diode (LD), high frequency/high power transistor and photodiode.
Generally, in the structure of the diode, an activity layer is formed on the junction between the P type and N type layers. When the activity layer is additionally positioned on the junction between the P type and N type layers, the structure will be called as a PIN photodiode (PIN PD). For the vertical design of the structure, the PIN diode comprises a homojunction structure, a heterojunction structure, and a quantum well structure. The heterostructure is often used for control the band gap depending on the properties itself.
The photodiode can transform a photo signal into an electric signal with low consumption. Therefore, the photodiode is suitable for being a light-receiving element to be used in the applications of light detection and light communication. For example, the photodiode can be used as a light-receiving element of a mouse, a photo coupler, a photo discontinuation/continuation, a remote controller, or a wireless transmission device. The reason for the photodiode can be a light detection device is that when the photons with energy greater than the band gap of the material are irradiated on the empty area of the diode, the originally-combined electron and electric hole will be separated because the electric forces exerted on them are opposite to each other. And the separated electrons and electric holes will separately flow into the P type and N type junction areas so as to form photo current. By being connected to an outside current amplifier, the photo current can be accurately measured wherein the magnitude of the photo current is directly proportional to the absorbed photons. Therefore, how to promote the light receiving ability of the photodiode by changing the band gap of the heterostructure is an important subject to be researched and developed in the related technology field. However, in the prior art, the technology for modulating the band gap of the photodiode is imperfect so that the light receiving ability is insufficient and the performance of the GaN photodiode element is poor.
Therefore, in order to resolve the mentioned problems, the present invention is provided to dope a proper amount of borons in the activity layer of the GaN-based diode so as to modulate the band gap between the P type and N type layers. Thus, the light receiving ability of the GaN heterostructure photodiode will be promoted.